@JeepCares The formal diagnosis was that the torque converter clutch started to come apart. The various bits of said converter were then free to enter the transmission and...that was that.
My local jeep dealership was no help once they found out it was not under warranty.
@JeepCares I have just been informed that my 2018 jeep grand cherokee will need a new transmission. It has less than 60k miles but is outside the 5 year power train warranty.
It's very frustrating that a car with so few miles should need new transmission.